Entangled Polymer Chains Research Articles

Characteristics of novel transparent poly(methyl methacrylate)/silica nanoparticle hybrid film prepared based on entanglement-agglomeration transition mechanism

Using polydisperse poly(methyl methacrylate) (PMMA) and SiO2 nanoparticles with an average particle diameter of ~15 nm, transparent PMMA/SiO2 hybrid films could be fabricated based on the agglomeration mechanism of nanoparticles in the suspension. The calculated distance between the particles in the transparent films was ~30 nm, corresponding to the actual measured value of 31 nm obtained from the small-angle X-ray scattering intensity. Upon heating the transparent hybrid films to 140 °C, above the glass-transition temperature of PMMA, the transmittance of UV light decreased significantly with the heating time for hybrid films with Mw=9.6 × 104 and a critical molecular weight (Mc) of 3 × 104 or greater, at which PMMA chains show effective entanglement. However, for hybrid films with Mw=0.3 × 104 and with the Mc or a lower molecular weight, the initial high transmittance was sustained over the entire wavelength range even after a long period of heating, and no agglomeration of the SiO2 nanoparticles was observed. Such molecular weight dependence was also observed for monodisperse PMMA/SiO2 hybrid films, leading to an examination of the difference in the rates of polymer chain entanglement and disentanglement. The critical molecular weight (Mc), at which the entanglement effect of the PMMA chain occurs is ~3 × 104. When the PMMA molecular weight in the hybrid suspension and film is such that Mc < Mw, such formation of molecular chain entanglements acts as a driving force for the agglomeration of SiO2 particles. In cases in which the PMMA molecular weight in the hybrid suspension and film is such that Mw< Mc, because no effective entanglements are formed, there is no driving force for the agglomeration of the SiO2 nanoparticles.

Orientation in multi-layer chitosan hydrogel: morphology, mechanism, and design principle.

Hydrogels with organized structure have attracted remarkable attentions for bio-related applications. Among the preparation of hierarchical hydrogel materials, fabrication of hydrogel with multi-layers is an important branch. Although the generation mechanism of layers had been fully discussed, sub-layer structure was not sufficiently studied. In this research, multi-layered chitosan hydrogel with oriented structure was constructed, and the formation mechanism of orientation was proposed, based on gelation behavior and entanglement of polymer chains in the hydrogel-solution system. Employing the layered-oriented characteristic, chitosan hydrogel materials with various shapes and structure can be designed and fabricated.

Effects of the Junction Functionality and Chain Entanglements in Chemomechanical Behavior of Polyelectrolyte Gels

By considering the functionality of junctions and entanglements of polymer chains for polyelectrolyte gels, a new free energy density function is presented via combining Edwards-Vilgis slip-link model with Flory-Huggins theory. On this basis, the effects of the functionality of network junctions and entanglements of polymer chains are systematically analyzed for free swelling of a cubic polyelectrolyte gel and constrained swelling of a blanket layer of the gel. Analytical results show that the functionality of junctions and chains entanglements plays an important role in the coupled chemomechanical deformation of polyelectrolyte gels.

Reptation and constraint release dynamics in bidisperse polymer melts

Bidisperse melts of linear, entangled polymer chains were studied using dissipative particle dynamics. The entanglement constraints were mimicked with our newly developed slip-spring approach. The compositions cover blends with short matrix chains, slightly above the molecular entanglement weight as well as blends were both chain lengths exhibit distinct entangled dynamics at various weight fractions. The Struglinsky-Graessley parameter Gr, which is the ratio between the relaxation time of the long chains due to pure reptation and the relaxation time of the tube caused by constraint release, ranges between values high above and below unity. We compare our slip-spring model with simulations that use conventional generic polymer models where bond crossings are prevented by excluded-volume interactions and find fairly good agreement in terms of the mean squared displacement. However, the slip-spring approach requires only a fraction of the computational time, making large scale systems feasible. The dynamical interference of the two different chain lengths is discussed in terms of reptation and constraint release dynamics. For bidisperse melt compositions with Gr < 1.0 the relaxation time of the long chain component is not affected by constraint release. However, for compositions where constraint release is supposed to contribute significantly to the relaxation mechanism (Gr > 1.0), we find strong evidence that the long chains reptate inside a dilated tube whose diameter increases with an exponent of 1/2 towards lower weight fraction of the long chains. Furthermore we observe a linear relation between the relaxation time and weight fraction. Therefore, based on the relaxation times, our results support the validity of the tube dilation model as proposed by Doi et al. [Macromolecules 20, 1900-1906 (1987)].

Operating window of solution casting. II. Non‐Newtonian fluids

ABSTRACTThe operating windows of the solution casting of two polymeric liquids were evaluated experimentally. The experimental setup and procedure were the same as used previously for the casting of Newtonian fluids (Journal of Applied Polymer Science 2013, 129, 507–516). Aqueous carboxymethylcellulose/glycerol solutions exhibited pure shear‐thinning behavior at low polymer concentrations but became viscoelastic at high polymer concentrations, whereas polyacrylamide/glycerol solutions showed viscoelastic behavior over a wide range of concentrations. The shear‐thinning behavior, in conjunction with a low level of elasticity, of the casting solution was found to be useful in expanding the stable operating windows. However, an opposite effect on the operating windows was found for highly elastic solutions. The non‐Newtonian effect on the maximum stable casting speed was prominent only when the capillary number exceeded unity. Defects outside of the operating window were mostly similar to those observed in Newtonian solution casting. For highly concentrated solutions, a new rough surface defect was observed. This defect could be attributed to polymer chain entanglement, alignment, or breakup. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41411.

The Study on Mechanical Properties of POSS Hybrid PVA Hydrogels

A novel POSS hybrid nanocomposite hydrogels were synthesized by introducing water-soluble Oa-POSS into the PVA hydrogels. The mechanical properties are obviously dependent on the composition of gels. With the increase of Oa-POSS, the tensile strength and modulus increases significantly while the elongation break decreases. The gels exhibit higher compression strength than pure PVA hydrogels. This phenomenon is attributed to the effective entanglement of polymer chains around nanoparticles and enhanced interaction between PVA chains.

Modification of cellulose nanocrystal-reinforced composite hydrogels: effects of co-crosslinked and drying treatment

The synthesis platform of composite hydrogels containing rigid reinforcing filler cellulose nanocrystals (CNCs) and polymer matrix polyacrylamide (PAM) has been proposed (Yang et al. in Cellulose 20:227–237, 2013). The features of CNCs as multifunctional crosslinkers and flexible polymer chain entanglements contributed to the unique arrangement of CNC/PAM clusters with reversible network structures. In this article, the chemical crosslinking agent N,N′-methylene-bisacrylamide (BIS) was added to obtain the dual crosslinked networks, and the mechanical properties of the resulting co-crosslinked hydrogels were examined by tailoring the CNC and BIS concentrations. The results indicated that the homogeneous dispersion of CNCs throughout the polymer matrix was disturbed in the presence of BIS, and the covalent crosslinkers led to weakness and brittleness of the hydrogels. Some new entanglements within the networks were formed after a simple drying treatment, which was verified by the greater tensile strength compared with the as-prepared ones. The mechanism for the formation of these new entanglements was ascribed to the irreversible rearrangement of the CNC/PAM network structure, whereas for co-crosslinked hydrogels no strength increment was observed after the drying treatment.

Coupled Effect of Orientation, Stretching and Retraction on the Dimension of Entangled Polymer Chains during Startup Shear

The theoretical description of how entangled polymers undergo large deformation has been at the heart of polymer dynamics. Over the years, the polymer physics community has adopted the tube model as the standard paradigm for describing polymer deformation and flow in both the linear and nonlinear regimes. The tube model envisions an ensemble of chains that undergo reptation and fluctuation inside smooth confining tubes on time scales of the Rouse relaxation time. It provides a reasonable and appealing description of the equilibrium and near equilibrium dynamics of entangled polymer melts and concentrated solutions. Some of the predictions based on this paradigm are also in apparent agreement with macroscopic rheological measurements for large deformations. However, some discrepancies with the tube model have been noted in the literature. For example, the time for the onset of time-strain superposibility in experiments has been shown to be much longer than the Rouse time anticipated based on the tube model. More recently, S.-Q. Wang’s group using particle-tracking velocimetry reported a number of nonlinear rheological phenomena that questioned the validity of the tube-model assumptions. The theoretical implications of the reported phenomena have been controversial.

Polymer Basics: Classroom Activities Manipulating Paper Clips To Introduce the Structures and Properties of Polymers

A simple and effective hands-on classroom activity designed to illustrate basic polymer concepts is presented. In this activity, students build primary structures of homopolymers and different arrangements of monomers in copolymer using paper clips as monomers. The activity supports formation of a basic understanding of polymer structures, tacticity, copolymers, degree of polymerization, arrangement of monomers in copolymers, and polymer chain entanglement.

Colloidal interactions of inorganic nanoparticles grafted with zwitterionic polymer brushes and gels by surface-mediated seeded polymerization.

A robust and straightforward approach is introduced to synthesize inorganic nanoparticles chemically grafted with a zwitterionic poly(2-methacryroyloxyethylphosphorylcholine) (PMPC) thin layers. The synthesis method is based on the surface-mediated seeded polymerization. In order to observe how the polymer chain architectures affect colloidal interactions, the zinc oxide nanoparticles are grafted with linear brushes and with a thin hydrogel layer, respectively. The thickness of PMPC shell layers spans a few nanometers. The studies on suspension rheology for the nanoparticles show that the nanoparticles with PMPC brushes show the stronger repulsive force than those with the PMPC gel shell due to the entropic stabilization. When the shear force is applied to the Pickering emulsion produced by assembly of the nanoparticles, it is noticeable that the presence of PMPC brushes on the particles rather enhances the drop-to-drop attraction, which presumably stems from the entanglement of polymer chains between the contacted interfacial planes of the emulsion droplets during shearing.

Concentration mediated structural transition of triblock copolymer ultrathin films.

X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement techniques are used to study the structural changeover as a function of concentration of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer diluted in toluene spin-coated as ultrathin films on hydrophilic Si substrate. A lamellar structure made of three alternating incomplete bilayers is observed until the concentration of copolymer solution attains a threshold value of about 3.6-4 g/L. Around this concentration and beyond, the entanglement of polymer chains takes place during drying and the growth of a homogeneous film made of complete bilayers on Si substrate is observed. The strong hydrophilic nature of the Si substrate dictates the growth of this amphiphilic copolymer. We evidence that the lower part of the films is made of hydrophilic PEO blocks attached to the substrate while the hydrophobic PPO blocks are directed toward air.

Effects of Polymer Viscosity and Nanofillers on Morphology of Nanofibers Obtained by a Gas Jet Method

Abstract This research evaluates the effects of molecular weight, polymer solution concentration, and carbon nanotube concentration on diameter distribution of polymer nanofibers produced with gas jet fiber (GJF) method. In GJF method, the shear and extensional forces of high-velocity gas jets are used to spin fibers from polymer solutions. The correlation between polymer molecular weight and fiber diameter distribution is studied along with the effect of multi-walled carbon nanotubes (MWCNT) on fiber diameter distribution. The paper also assesses how carbon nanotubes distribute in bi-component polymer nanofibers. It is found that polymer chain entanglement is a key determinant of fiber diameter. MWCNTs do not show preference for distribution in polyvinylidene pyrrole (PVP) and polyvinylacetate (PVAc) and instead appear on the surfaces of the fibers. A negative value of spreading coefficient supports this observation.

Entropy-Driven Pattern Formation of Hybrid Vesicular Assemblies Made from Molecular and Nanoparticle Amphiphiles

Although an analogy has been drawn between them, organic molecular amphiphiles (MAMs) and inorganic nanoparticle (NP) amphiphiles (NPAMs) are significantly different in dimension, geometry, and composition as well as their assembly behavior. Their concurrent assembly can synergetically combine the inherent properties of both building blocks, thus leading to new hybrid materials with increasing complexity and functionality. Here we present a new strategy to fabricate hybrid vesicles with well-defined shape, morphology, and surface pattern by coassembling MAMs of block copolymers (BCPs) and NPAMs comprising inorganic NPs tethered with amphiphilic BCPs. The assembly of binary mixtures generated unique hybrid Janus-like vesicles with different shapes, patchy vesicles, and heterogeneous vesicles. Our experimental and computational studies indicate that the different nanostructures arise from the delicate interplay between the dimension mismatch of the two types of amphiphiles, the entanglement of polymer chains, and the mobility of NPAMs. In addition, the entropic attraction between NPAMs plays a dominant role in controlling the lateral phase separation of the two types of amphiphiles in the membranes. The ability to utilize multiple distinct amphiphiles to construct discrete assemblies represents a promising step in the self-assembly of structurally complex functional materials.

Structure, dynamics and primitive path network of polymer nanocomposites containing spherical nanoparticles

ABSTRACTWe investigate the effect of nanoparticles on polymer structure, polymer dimensions and topological constraints (entanglements) in polymer melts for nanoparticle loading above percolation threshold as high as 40.9% using stochastic molecular dynamics (MD) simulations. We show unambiguously that short polymer chains are not disturbed by the presence of repulsive nanoparticles. In contrast entangled polymer chains can be perturbed by the presence of attractive nanoparticles when the polymer radius of gyration is larger than the nanoparticle radius. They can expand under the presence of attractive nanoparticles even at low nanoparticle loadings of very small nanoparticle size. We observe an increase in the number of entanglements (decrease of Ne with 40.9% volume fraction of nanoparticles dispersed in the polymer matrix) in the nanocomposites as evidenced by larger contour lengths of the primitive paths. Attraction between polymers and nanoparticles affects the entanglements in the nanocomposites and alters the primitive path.

Investigation of the Influence of Nanoclay on the Mechanical, Thermal, and Morphological Behaviors of Polyurethane/Ginger Spent Hybrid Composites

ABSTRACTWith an objective to investigate the influence of nanoclay (NC) on the mechanical, thermal, and morphological properties of polyurethane (PU) in the presence of 5 wt% of ginger spent (GS), PU/GS/NC nanocomposite films were fabricated by a solution intercalation method with varying amounts, namely 0, 0.5, 1.0, and 2.0 wt%, of NC. The fabricated PU/GS/NC nanocomposite films were characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The mechanical properties such as the tensile strength, tensile modulus, percentage elongation at break, and surface hardness have been performed for nanocomposites. FT‐IR and XRD analysis show the nature of the NC interaction with the PU matrix, whereas SEM images show agglomeration of NC and entanglement of polymer chains with NC with an increase in the NC content. It was found that the tensile strength of the biocomposites increased from 4.5 to 13.7 MPa, tensile modulus increased from 8.2 to 14.3 MPa, and surface hardness increased from 70 to 77 shore A, whereas the percentage elongation at break decreased from 155.2% to 100.5%. Static water contact angle measurements on the surface of the PU/GS/NC nanocomposites reveal a reduction in surface polarity by way of changes in the contact angle from 76.83° to 55.24°, whereas surface energy increased from 88.36 to 102.11 mJ/m2 with an increase in the NC content. With an increase in the NC content, the chemical resistance of the green composites in different chemical environments improved. Thermal analysis by a thermogravimetric analyzer indicates improvement in thermal stability with an increase in the NC content. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2014, 33, 21404; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21404

Design of electrospayed non-spherical poly (l-lactide-co-glicolide) microdevices for sustained drug delivery

Polymer chain entanglements in organic solvents can be considered akey parameter in theformation of non-spherical beads when electrospraying is employed. The shape of micro/nanometric drug delivery systems plays a major role since it can affect circulation, extravasation, distribution and in vivo clearance of the devices. In this frame, we investigated the influence of polymer processing parameters on the design of polylactic-co-glycolic acid non-spherical microdevices loaded with triamcinolone acetonide (TrA),a sparingly water soluble corticosteroid, prepared by electrospraying technique through a one-step process. In particular, we verified that the formation of non-spherical MDs is related to the presence of entanglements among polymer chains to select the optimal solution to be sprayed. The addition of TrAdid not substantially affect the particle morphology in terms of size, size distribution and circularity at all the tested drug loadings. Furthermore, the drug could be released for a prolonged period, with controlled and reproducible kinetics for over 3weeks. The mathematical modeling of release profiles highlighted that the release is mainly driven by degradation, at a higher extent in the case of low drug loading.

The effect of carboxylated multi-walled carbon nanotubes on reinforcement efficiency of thiazole-bearing poly(amide-imide) composites

Multi-walled carbon nanotube (MWCNT)/amino acid-based poly(amide-imide) (PAI) composites containing pendant thiazole moiety were successfully prepared through ultrasonication-assisted solution blending. In order to improve the compatibility between the PAI and MWCNTs, carboxylated MWCNTs were used in this study. The mechanical and thermal properties and cross-sectional morphology of the composites were investigated. The incorporation of MWCNTs–(COOH)n improved the mechanical properties of the composites compared with that of neat PAI. An improvement in thermal properties of the MWCNT/PAI composites was also observed. This synergetic enrichment in mechanical and thermal properties of the composites is due to the increased interfacial interactions resulted from the improved dispersion state and entanglement of polymer chains, as revealed by electron microscopy observation.

Hyaluronic acid colloidal gels as self‐assembling elastic biomaterials

Hyaluronic acid (HA) is a naturally occurring biodegradable polymer with a variety of applications in medicine. The use of HA as a filler or scaffold for regenerating tissues often requires improving the elastic properties of HA. This is conventionally accomplished via chemical crosslinking, which might require the generation of toxic free radicals. Although the mechanical properties of the resulting gel material can be tuned, these types of materials are static and susceptible to mechanical failure. The aim of this study was to develop a colloidal system for scaffold fabrication that is held together by physical interactions between HA nanoparticles. HA nanoparticles composed of 17 kDa HA suspended in water at different concentrations (15%, 30%, and 45% w/v, respectively) formed a stable three-dimensional (3D) colloidal gel as a result of physical entanglement of free polymer chains on the surfaces of nanoparticles. The swelling ratio, shear moduli (G), compressive failure properties, and viscosity of colloidal gels were concentration dependent. The colloidal gels also were found to exhibit dynamic and recoverable properties, thus suggesting that these "self-associating colloids" offer characteristics distinct arising from crosslinked polymers or high concentration colloids.

Study of translational dynamics in molten polymer by variation of gradient pulse-width of PGSE

Pulsed gradient spin echo is a method of measuring molecular translation. Changing Δ makes it sensitive to diffusion spectrum. Spin translation effects the buildup of phase structure during the application of gradient pulses as well. The time scale of the self-diffusion measurement shortens if this is taken into account. The method of diffusion spectrometry with variable δ is also less sensitive to artifacts caused by spin relaxation and internal gradient fields. Here the method is demonstrated in the case of diffusion spectrometry of molten polyethylene. The results confirm a model of constraint release in a system of entangled polymer chains as a sort of tube Rouse motion.

Specific features of the polyelectrolyte behavior of weakly charged cryogels of polyacrylamide and poly(N-isopropylacrylamide)

Specific features of the polyelectrolyte behavior of weakly charged common gels and cryogels of copolymers of polyacrylamide and poly(N-isopropylacrylamide) with sodium acrylamido-2-methyl-1-propyl sulfonate are investigated. The cryogels are synthesized in frozen solutions at −15°C. It is shown that the polyelectrolyte swelling is significantly weaker in the case of cryogels than that in the case of gels synthesized in solutions. For thermosensitive gels with isopropylacrylamide groups, collapse occurs during heating. Charging of a common gel leads to a noticeable (18°C) increase in the transition temperature. For a cryogel, this growth is 3°C. During the interaction with cetylpyridinium chloride, the gel contraction is much more pronounced for common weakly charged gels. At the same time, walls of pores of a collapsed cryogel contain a smaller amount of the solvent. Isotherms of the adsorption of a cationic surfactant by anionic common gels and cryogels differ insignificantly. Model gels synthesized in concentrated acrylamide solutions exhibit very weak polyelectrolyte swelling, similar to that of cryogels. The behavior of cryogels is explained by a very high local concentration of crosslinks due to a strong entanglement of polymer chains.